Portland cement is one of the most important materials in the construction industry because of its multiple applications and mechanical and physical properties. The current production rate for Portland cement is about two billion tons per year and is predicted to increase to about 3.5 billion tons per year by 2015. However, the costs and volume used are important factors that have led to a search for new materials for replacing a part of the cement and for new materials that will lead to improved products.
A problem with the use of Portland cement is that the production of Portland cement is highly energy intensive with a significant environmental impact. For example, the production of one ton of Portland cement produces about one ton of carbon dioxide into the atmosphere or about seven percent of the global carbon dioxide emissions. Therefore, there is a pressing need for developing green building materials to fulfill the increase in demand for Portland cement.
High performance concrete consumes high cement content namely about 500 kg/m3. Consequently, concrete producers frequently blend cement with pozzolan materials such as fly ash, silica fume and ground granulated blast furnace slag. The pozzolan materials have become very relevant due to their capacity to interact with the cement components and to improve its properties. The pozzolans are siliceous or silica-aluminous materials that in themselves have little or no cementitious value, but in finely divided form and in the presence of moisture chemically react with calcium hydroxide at ordinary temperatures to generate compounds possessing cementitious properties.
Pozzolan materials such as silica fume and fly ash are considered to be basic materials for the production of high performance concrete. However, costs for these materials have increased and their availability threatens to pose problems for the sustainable production of certain concrete products. Consequently, there is a need for less expensive materials for the partial replacement of cement in concrete products. It has also been recognized that civil construction applications such as roads, bridges, commercial and residential buildings, etc. that require significant amounts of cement based concrete would benefit from a lower cementitious material that reduces the demand for cement and dependency on the availability of pozzolan materials.
Researchers have attempted to find cheaper and more readily available materials as partial replacements for cement. For example, a U.S. Pat. No. 5,820,668 of Comrie discloses an inorganic binder composition that may be used in partial substitution for Portland cement. The inorganic binder composition includes materials such as fly ash, Al2O3, pozzolan, ground slag, nephelene cyanite, anhydrous aluminum silicate, hydrous aluminum silicate, hydrous sodium hydroxide, silicic acid, potassium salt, and sodium salt.
A more recent U.S. Patent Application Publication No. 2005/016096 of Comrie also discloses cementitious materials including stainless steel slag and geopolymer that can be added to conventional cement compositions, such as Portland cement as a partial or total replacement for conventional cement materials. The stainless steel slag may comprise silicates and/or oxides of calcium, silicon, magnesium, iron, aluminum, manganese, titanium, sulfur, chromium and/or nickel. The geopolymer may comprise aluminum silicate and/or magnesium silicate. In a preferred embodiment, curing of concrete materials by the action of water on the cementitious materials is enhanced with the addition of an activator component selected from calcium bromide, calcium nitrate, calcium nitrite, calcium chloride, calcium oxide, and sodium bromide.
Even more recently a U.S. Patent Application Publication No. 2011/0048287, incorporated herein in its entirety by referenced, published on Mar. 3, 2011 relates to a cement/aggregate composition, concrete product and method for making a concrete product wherein the concrete product is produced by providing red dune sand having a particle size of 45 microns or less and mixing the red dune sand with a hydraulic cement in a ratio of about 30 percent of the cement being replaced by the red dune sand. The cement and red dune sand are then mixed with fine and coarse aggregate, water and a superplasticizer and cast after pouring into a mold cavity. Then within 24 hours of casting the cast article is steam cured for 12 hours under atmospheric pressure, demolded and placed in an autoclave at 100 percent humidity. The temperature in the autoclave is raised to 180° C. within one to two hours and maintained at that temperature for four to five hours. The temperature also increases the pressure to about 10 bars. The pressure is released to reach atmospheric pressure within 20 to 30 minutes and the temperature reduced gradually so that the article can be removed.
Dune sand is an abundant natural material and is found in many parts of the world. The sand is rich in silicon dioxide (SiO2), but in the less reactive form. One approach to utilize the dune sand as cement replacement material was disclosed in a previous U.S. Patent Application Publication No. 2011/0048287 of Alhozaimy et al. As disclosed therein the milled or ground dune sand has a particle size of about 45 microns or less and is used as a partial replacement of up to 30 percent of the cement to provide concrete with comparable strength to plain concrete. The 30 percent replacement of cement by milled dune sand was considered to provide a sufficient amount of silica (SiO2) that can react with Ca(OH)2 generated from the 70 percent of cement to produce products having cementitious properties.
The use of a combination of naturally available dune sand and limestone after milling or grinding have shown potential as a replacement for up to 85% of the Portland cement in concrete products.